Answers for "how to use the mainaxisalignment in multi colum in flutter"

next row column in flutter

var phoneNumber = new Row(
  mainAxisSize: MainAxisSize.min,
  children: <Widget>[
    Expanded(
      child: new Padding(
        padding: const EdgeInsets.all(20.0),
        child: countryCodePicker,
      ),
    ),
    Expanded(
      child: new Padding(
        padding: const EdgeInsets.all(20.0),
        child: mobileNumber,
      ),
    ),
  ],
);

align column to center of flex flutter

// If you want the whole table to be Centered, use the mainAxisAlignment property of Column.
///Column
mainAxisAlignment: MainAxisAlignment.center //Center Column contents vertically,
crossAxisAlignment: CrossAxisAlignment.center //Center Column contents horizontally,

///Row
mainAxisAlignment: MainAxisAlignment.center //Center Row contents horizontally,
crossAxisAlignment: CrossAxisAlignment.center //Center Row contents vertically,